Voltage regulation



Dec. 31, 1940. A KUNTKE 2,227,353

VOLTAGE REGULATION Filed Jan. 14, 1939 By@ .6. /amm Patented Dec. 31, 1940 PATENT OFFICE VOLTAGE REGULATION Alfred Kuntke, Eindhoven, Netherlands, assignor, by mesne assignments, to Hartford National Bank and Trust Company, Hartford, Conn., as

trustee Application January 14, 1939, Serial No. 251,049 In Germany January 27, 1938 6 Claims.

My invention relates to a circuit arrangement for maintaining the voltage across a load .at a constant value.

As my invention is particularly advantageous for controlling the voltage across an X-ray tube, I shall describe the same in this connection. However, the invention is not rlimited. thereto, but may be used to control the voltage across other types of loads which are supplied from a source of variable voltage.

It is known to maintain the voltage across a load at a substantially constant value by using a circuit arrangement in which the .load is supplied through a grid-controlled control tube Whose grid is supplied with a, voltage which is in a given ratio tol the variations of the voltage across the load. The resistance of this tube is varied in such a manner that the eurent through the tube remains substantially constant, and variations in the voltage of the supply source are taken up mainly in the tube and only to a small percentage by the load. In order to make it easier to maintain the load voltage at a constant value, it has been proposed to use in such circuits an amplifier tube whose grid and cathode are connected to the terminals of the load and whose vplate circuit comprises a resistance, the voltage across this resistance being applied between the grid and cathode of the control tube. f

The main object of my invention is to improve such circuits.

A further object is to provide a circuit arrangement which is Iparticularly adapted vto control the voltage across an X-ray tube.

A still further object is to provide a circuit arrangement in which the voltage across the load can be maintained at a predetermined value even when the voltage of the supply source very closely 40 approaches this value.

Further 'objects and advantages of the invention will appear as the description progresses.

In acordance with the invention I use the plate Voltage of the amplifier tube as a negative grid voltage in the `grid circuit of the control tube, and so control the amplifier tube that the grid potential thereof is dependent upon the terminal voltage to be maintained constant, and in contradistinction to known'arrangements, increases with decreasing terminal voltage.

In such a circuit arrangement the control tube is placed at a fixed grid voltage, which makes it of particular advantage in controlling the voltage of an AX-ray tube. More particularly, with the instantaneous loads occurring in the opera.

(ci. 25o-102) tion of such tubes, it is desirable that the voltage of the tube be at its correct value at the start. If the grid circuit of the control tube should include a high resistance this would not be possible because the grid voltage of this tube, A5

because of the internal capacity between the anode and the grid thereof, might be greatly influenced by the variation of the anode voltage of the tube.

The circuit arrangement according to the invention has the additional advantage that the internal resistance of the control tube can be reduced to a Very low value. As a result, the terminal voltage of the load can be maintained at the desired predetermined value even when the voltage of the current supply has become very close to this value. This, of course, is particularly advantageous in the case of an X-ray tube which is supplied with operating voltage by a discharging condenser.

With the circuit arrangement according to the invention there are no supplementary resist ances connected in series with the source of current that supplies the grid currents, and consequently, grid currents of considerable strength can ow if a positive grid voltage is used. As a result the resistance ofthe control tube can be reduced to a very large extent, and in the case of an X-ray tube supplied by a charged condenser, the energy content of the condenser can thus be utilized more efficiently, and thus a smaller condenser can be used for a given exposure-energy.

In order that the invention may be clearly understood and readily carried into effect, I shall describe the same in more detail with reference to the yaccompanying drawing, in which the single ligure is a schematic Wiring diagram of a circuit arrangement according to the invention.

The arrangement illustrated comprises a load 2 in the form of an X-ray tube having an anode I8 and a cathode I'l, a condenser I serving as a supply source of variable voltage, a control tube 3 having a grids a plate 20 and a cathode IU, and an amplifier ytube 4 having a cathode II, a grid I3 and a plate I2.

Condenser I is charged by a charging arraz'igementv 2l, and as such arrangements are well known in the art, further description of the same is believed unnecessary. A suitable charging circuit is illustrated in the U. S. Patent #1,954,612 to Albert Bouwers. Condenser I has one terminal connected through a conductor 22 to the cathode I'I, and has its other terminal connected to the plate 20 of tube 3 Whose, cathode I is connected through a conductor 23 to anode I8 of the X-ray tube. Thus, control tube 3 is connected in series with the X-ray tube and condenser, and takes up the potential difference between the variable supply voltage of the condenser and the load voltage across the X-ray tube.

Connected in parallel with the X-ray tube is a series circuit comprising a potentiometer having a xed resistor 'I and a variable resistor 6 provided with a sliding contact I4, an anode resstor 8, and an auxiliary current source I5, shown as a battery.

The amplifier tube 4 has its cathode I connected to grid 9 of tube 3 and to one terminal of an auxiliary current supply 5 whose other terminal is connected to a point 24. Supply 5 is shown as a battery, but the well-known combination of a transformer and rectiyingsmoothing device may be used. riihe grid I3 is connected through a conductor to a point 2'3 between resistors E and 1.

As indicated by lines of different widths and by the arrows, in operation a heavy current may flow through the X-ray tube 2, and a low current may flow through the amplifier tube 4 and resistances 6 and l. Furthermore, a current Will flow from the auxiliary current source 5 through resistance 8 to the amplifier tube 4. As the grid I-S is connected to point 25 on the potentiometer, the potential thereof will be dependent upon the high tension across the X-ray tube.

The voltage difference between grid' i3 and cathode II is composed of two parts; the voltage across the auxiliary source of current 5 and .he voltage across resistance 5. The first cornponent part of the grid voltage is positive, the second component part of the grid voltage is negative. Consequently the potential of grid I3 will increase relative to the potential of cathode Il when the voltage across the X-ray tube 2 and thereby the voltage across resistance 6 decreases.

In practice the resistor 8 may have a resistance of about 105 ohms, resistor 'I a resistance of about megohrns, and resistor 6 may be adjusted hy sliding the contact I4 to a resistance of about l to 3 megohrns. The auxiliary current source 5 may have a voltage of about 2,000 volts, and the predetermined value cf the voltage to be applied across the X-ray tube may be between 40 and 90 kilovolts.

In practice a condition is set up under which the voltage drop across the resistor 6 is about eoual to the voltage across the auxiliary source of current 5. The terminal voltage of the X-ray tube is maintained constant at a value ER which may be expressed by the following equation:

EH-ETTG in which, E5 is the voltage of the auxiliary source of current 5, and Re and R7 are the resistances of the resistors 5 and I respectively.

By controlling the value of the resistor 6 (Re) it is possible to vary the voltage applied across the X-ray tube (ER) so that the circuit arrangement according to the invention allows the voltage to be controlled in any easy manner.

If, due to the derival of current, the voltage of the condenser should approach the tube voltage (En), the voltage drop in the tube 3 should become as small as possible in order that the tube voltage can be retained at the desired value. For this purpose it is necessary that a positive voltage be applied to the grid of the tube 3, which involves the use of a considerable grid current. To supply this grid current, the source of bias voltage I5 is used and is so calculated that if the grid voltage of tube 4 is equal to Zero, it can cause a considerable current to ilow through this tube. Since the grid circuit of tube 3 does not include a considerable ohmic resistance, the internal resistance of control tube 3 can thus be reduced to a negligible value.

Under these circumstances and the above mentioned values of resistances and auxiliary voltage being provided, the voltage across the X- ray tube, set to a predetermined value of kv., will not decrease by more than 5% as along as the condenser voltage is 500 volt in excess of the tube voltage.

As shown, the source of bias voltage I5 is connected between the cathode ID of the control tube 3 and the anode I2 of the amplier 4. Such an arrangement is preferable because the grid capacity of the control tube 3 may be a minimum and the grid voltage may be maintained as stationary as possible. More particularly, in the event of rapid potential variations, the internal capacity of source I5 exercises less influence on the grid voltage of the control tube 3 than if source I5 were connected between the grid 9 and the cathode II.

Connected across the cathode II and grid I3 is a single-throw single-pole switch I6 and a current source I9. If switch I6 is closed a negative potential will be applied to the grid I3 by the current source I9 so that tube 4 will not permit the passage of current; the grid S being highly negative no current will pass through control tube 3 and X-ray tube 2. If switch I5 is opened, the X-ray tube is set in opera-tion and a voltage in accordance with the above equation is applied across the same.

While I have described my invention with reference to a specic embodiment and in connectiono with an X-ray tube, I do not wish to be limited thereto but desire the appended claims to be construed as broadly as is permissible in view of the prior art.

What I claim is:

l. A circuit arrangement for maintaining co1- stant the terminal voltage of a load supplied from a source of variable voltage, comprising a control tube connected between said load and source and having an anode, a cathode and a. grid` a grid circuit for said control tube, an amplifier tube having a grid, said amplifier tube being connected in said grid circuit and with the voltage across the same acting as a negative grid voltage, and means associated with the load to vary the potential of the grid of the amplifier tube with the terminal voltage of the load and to thereby vary the potential of the grid of the control tube and decrease the voltage difference between the grid and anode of the control tube when thc terminal voltage of the load decreases.

A circuit arrangement for maintaining constant the terminal voltage of an X-ray tube supplied from a charged condenser, comprising a control tube connected between said X-ray tube and condenser and having an anodeA a cathode and a grid, a grid circuit for said control tube,

an amplifier tube having a grid, said ampiifier c Iii) the X-ray tube and to thereby vary the potential of the grid of the control tube and decrease the voltage difference between the grid and anode of the control tube when the terminal voltage of the X-ray tube decreases.

3. A circuit arrangement for maintaining constant the terminal voltage of a load supplied from a source of variable voltage, comprising a control tube connected between said load and source and having a grid, a grid circuit for said control tube, an amplifier tube having a grid, a potentiometer having a tap connected to the grid of said amplifier tube, an auxiliary current source, said amplier tube, currentsource and potentiometer being connected in the order named to form a series connection, said series connection being connected in parallel with the load, and a resistance shunting said amplier and auxiliary current source.

4, A circuit arrangement for maintaining constant the terminal voltage of a load supplied from a source of variable voltage, comprising, a control tube connected between said load and source and having an anode, a cathode and a grid, a grid circuit for said control tube, a source of positive bias in said grid circuit and on the cathode side, an amplifier tube having a grid, said amplier tube being connected in said grid circuit and with the voltage across the same acting as a negative grid voltage, and means associated with the load to vary the potential of the grid of the amplifier tube with the terminal voltage of the load and to thereby vary the potential of the grid of the control tube and decrease the voltage diierence between the grid and anode of the control tube when the terminal voltage of the load decreases.

5. A circuit arrangement for maintaining constant the terminal voltage of a load supplied from a source of variable voltage, comprising a control tube connected between said load and source and having an anode, a cathode and a grid, a grid circuit for said control tube, an ampliiier tube having a grid and a cathode, said amplifier tube being connected in said grid circuit and with the voltage across the same acting as a negative grid voltage, means associat/ed with the load to vary the potential of the grid of the amplier tube with the terminal voltage of the X-ray tube and thereby vary the potential of the grid of the control tube and decrease the voltage diierence between the grid and anode of the control tube when the terminal voltage of the X-ray tube decreases, and means to interrupt the flow of cul'- rent through the load including a source of negative grid potential adapted to be connected between the cathode and grid of the amplifier.

6. A circuit arrangement for maintaining constant the terminal voltage of an X-ray tube supplied from a charged condenser, comprising a control tube having a plate, a cathode and a grid, a plate circuit for said tube including said condenser and X-ray tube, an amplier tube having a grid, a cathode lconnected to the grid of said control tube and an anode connected to the Acathode of said control tube, an auxiliary current supply and a resistor connected in series across the cathode and anode of said amplifier, a potentiometer having a tap, said potentiometer and resistor being connected in series across said load, and a connection between said tap and the grid of the ampliiier.

ALFRED KUNTKE. 

